Inside Leopard's Time Machine: Backups for the rest of us

Think backups are a bore? Think again

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For a little more control


While Time Machine doesn't technically require any intervention once a backup drive is selected, it does offer a couple of options via System Preferences. The first is the option to change the hard drive on which Time Machine stores its backups. The other is to skip specific locations when performing backups.

Time Machine preferences

The Time Machine System Preferences pane. (Click for larger view.)

To change where Time Machine stores backups, just click the Change Disk button, and then select a different hard drive. You can choose internal or external hard drives, as well as individual hard-drive partitions. Be aware that if you change the backup disk, your existing backups will not be copied to the new drive, and a new initial backup will be performed.

Choosing a backup drive.
Choosing a backup drive. (Click for larger view.)

Obviously, the best choice for a backup drive is external, as it is a separate component from the internal drive(s) and drive controller of your Mac and thus more likely to survive corruption of the internal drive's directory structures, physical hard drive failures and other hardware damage that might occur to the computer.

Secondary internal drives (available only on PowerMac G4/G5 and Mac Pro towers) are more secure options than hard drive partitions but can still be affected by damage to a computer. Partitions are the least secure because they are physically part of the same drive, and any physical failure of that drive will render all partitions unusable.

By default, Time Machine excludes several folders used by Mac OS X for temporary files -- including Web browser and other application caches -- from backups. This makes perfect sense as a means to save space, since the operating system doesn't require these files to be maintained from one session to another.

The list of folders/directories excluded by default includes:

  • /Library/Caches and ~/Library/Caches
  • ~/Library/Mirrors
  • /tmp
  • /Library/Logs and ~/Library/Logs
  • Network and device mounts (/Volumes, /home, /dev, /Network, /net)

You can also opt to exclude additional files, folders, hard drives/partitions (by default, Time Machine will back up all connected hard drives and partitions in addition to your start-up drive) and system files.

Note: Home folders encrypted using FileVault are backed up only when the owner is logged in, which is the only time they are decrypted. They are encrypted in Time Machine backups so that only the owner or someone with a master FileVault password for a computer can access or restore them.

If you choose not to back up Mac OS X system files, you can save a couple of gigabytes of space on your backup drive. For the most part, however, these files don't change that frequently (the main exception being when Software Update is run). So you will save some space and time with your initial backup, but over the long run, that savings probably won't be significant.

Choosing not to back up system files also means that you will not be able to use Time Machine to completely restore a failed hard drive. Instead, you will need to reinstall Leopard and then restore your applications and user files. Because of this, we recommend not excluding system files.

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